In digital data processing systems, reliability of performance is a paramount consideration. The prior art is replete with efforts to insure and enhance reliability. Some of these techniques, though useful, are costly to implement, or are suitable only for systems of particular types. In recent times, with the advent of microcomputers, which provide the basis for low cost personal computer systems, a need has developed for inexpensive diagnostic techniques. Typically, microcomputer systems used in so-called "personal computers" employ video displays for providing output and disk storage devices (particularly so-called "floppy" disk storage devices) for providing mass-memory.
It is therefore an object of the present invention to provide an inexpensive diagnostic system for testing the operability of video output and secondary storage facilities for data processing systems, such as microcomputer systems.